Electric heating of liquid baths



lo 158,347, flied August 10,

Patented Dec. 24, 1940 UNITED STATES lPATENT OFFICE 2,225,617 ELECTRIC HEATING OF LIQUID BATHS Edouard Virgile Borel, Romont, Switzerland, and

Yvan Peyches, Paris, France,` assignors to Societe Anonyme des Manufactures des Glaces &

Cil-ey, Paris, France oduits Chimiques de Saint-Gobain, Chauny &

15 Claims.

The present invention relates to devices for the heating of liquids of the type in which heat is produced by causing electric current to flow through the mass of liquid. The invention is more especially, although not exclusively, concerned with devices of this kind for the heating of molten glass and is in part an improvement of the method and means described in the co-pending patent application of E. V. Borel, Serial No.

In devices of this kind, the heating treatment is generally intended to produce a transformation of the liquid matter. In particular, in glass tank furnaces for the continuous production of i5 glass, the raw materials, introduced at one end of the tank,'undergo, together with the molten mass, the successive melting, fining and cooling treatments as they flow along the tank. For each of these operations, the mass is to be subjected 20 to predetermined temperatures.

Now, in a substantially homogeneous liquid heated by electric current flowing through said liquid between electrodes, the heating effect at any point of the liquid depends upon the cur- 25 rent density at this point, which in turn depends upon the shape of the equipotential surfaces in the liquid mass.

In glass furnaces as heretofore constructed,

which are electrically heated by single phase or pclyphase current at a given voltage, the current density -at a given point can be varied only within narrow limits and in many cases by varying the position of the electrodes in a manner 35 which is, for other reasons, undesirable.

' For instance, when it is desired to heat a given length ofthe tank between a pair of electrodes, the power expended and therefore .the heating effect are determined by the size of the tank and the distance between Athe electrodes and it can be increased or reduced by increasing or reducing the length between the electrodes. When it is desired to lo'calise the heating action close to the electrodes by reducing their size, the

45 power consumed is thereby reduced. As a rule,

it is hardly possible to concentrate the heating in layers close to the surface of theliquid vwithout placing the electrodes so closeto each other that the heating is excessive. On the other hand, in

50 the case of polyphase` current, in order to distribute the load equally between the electrodes, it is generally necessary either to position the electrodes so that the resistances between them are equal, which is often an undesirable arrangement,

55 or to make them of different respective sizes,

which can produce a too high localised heating I at one of these electrodes.

It has also been suggested to modify the current density in the mass of glass by providing therein bodies or walls which reduce the cross sectional area through which the current flows. But these bodies are objectionable in that they cool the mass of glass and are liable to contaminate it.

The object of the present invention is to provide a device for heating a liquid bath and in particular molten glass, by controllingthe current density and therefore the heating at different points of the liquid, which avoids the above mentioned drawback and in particular which does not require changing the shape of the furnace or the position of the electrodes therein.

With this, and other, objects in view, according to an essential feature of the present invention, one or more bodies of a conductivity greater than that of the liquid are immersed in the mass of the liquid in which are located two electrodes of different polarity, so as to increase the conductivity of the bath between said electrodes, or, more generally, the conductivity of the bath from one electrode to the other. These bodies may be of a conductivity so much greater than that of the liquid that their surfaces are substantially equipotential surfaces.

According to another feature of the present invention, two bodies of a conductivity higher than that of the liquid may be immersed therein in different positions relatively to each other and to the electrodes, and short-circuited.

Other features of the present invention will result from the following detailed description of some specific embodiments thereof.

Preferred embodiments of the present invention will be hereinafter described, with reference `to the accompanying drawings, given merely by.

way of example, and in which:

Fig. 1 is a diagrammatic longitudinal vertical section of a furnace made according to the pres-l Figs. 5 and 6;

F185. 8, 9, and 11 are longitudinal sectional close to said rods.

views of a furnace according to the invention. for three-phase supply, showing different modioations of the arrangement of the electrodes and conductors.

In the arrangement shown by Fig. 1, the furnace l contains a bath of a liquid and in particular of molten glass 2, and two electrodes 3 extending transversely to the length of the tank at a small distance below the glass level. Three rods 4, of a material of a conductivity higher than that of glass, are immersed in the bath between the electrodes. These rods 4 are for example of graphite. The conductivity of the glass bath is increased along the path extending from one electrode to the rods 4, while the conductivity along other paths extending through the glass from one electrode to the other remainunchanged. Consequently, the current density along the rst mentioned path is increased and also the heating eifect along this path.

Now, in a glass furnace it is often advantageous toconoentrate the heating action near the glass.

surface. According to the present invention, this advantage is ensured by posi-tioning rods 4 at a small depth below the glass surface, without having to modify the position of electrodes 3.

Further when rods 4 are made of a material oi' a high conductivity as compared to that of the liquid, for instance in the case of graphite rods immersed in is substantially equipotential and the current density close to each of these surfaces is generally higher than at the points of the bath which are at a greater distance from the surface of said rods. Consequently, the heating eiTect is concentrated close to the rods as indicated by the lines of current ow 5.

Furthermore, as the total conductivity between electrodes I is increased by the provision of -rods 4. the power supplied to the mass of glass for a given voltage on the electrodes is increased.

Thus, by providing conducting bodies such as rods 4, immersed in the liquid mass, the heating eifect can be concentrated along any desired path between the electrodes, and in particular Also, the total power supplied by electrodes arranged in a given position and subjected to a given voltage can be modified, according to the invention, by immersing bodies such as rods 4 in the mass of liquid.

In the embodiment illustrated by Fig. 2, rods 4 are located merely in the central part of the width of the furnace, being supported by end portions 6 which may be constituted by extensions of the rods covered with an insulating ma- With this arrangement, the heating eiect is concentrated more in the central portion ofthe tank than close to the walls thereof, as shown by the lines o tcurrent flow 5.

In the embodiment of Fig. 3, two rods 4 are short-circuited on the outside of the furnace by conductor 1 and consequently, these two rods can be substantially at the same potential, so thatf the heating action can be substantially avoided between the rods 4, i. e., confined to the two regions between each of these rods 4 and the adjacent electrode l. As far as the heating action is concerned, this arrangement is thus equivalent to the existence of a single conducting body immersed in the bath and occupying the whole space between rods 4. With such an arrangement, the power consumed in the two regions above mentioned is considerably higher other and passing through.

, be unequal.

glass, the surface of each rod than would be the power consumed in the whole region extending between the electrodes in the absence in said region of rods 4.

In the embodiment of Fig. 4, these short-circuited rods 4 serve to prevent the flow of current through portion 8 of the furnace, where the sec tion is reduced, thus avoiding excessive heating in this portion 9 as would occur in the absence of said rods 4.

In the embodiment of the present invention illustrated by Figs. 5, 6 and 7, the -three electrodes 9. I0 and il are connected to the respective poles of a three-phase source oi current, and they are located in a horizontal plane vclose to the surface of the bath in order to ensure a distribution of hea-t which is often desirable. Furthermore, the electrodes may be in certain cases so dimensioned as to concentrate heat close to the electrodes, while ensuring heating of the mass of glass between the electrodes. With such an arrangement of the electmdes, which corresponds to a desired distribution of heat, and in the absence of bars 4, the resistance in the phase between electrodes 9 and Il would be generally greater than in the two other phases, between electrodes 9 and I0 and between l0 and Il, so that the loads on the three phases would But with the provision of the two bars 4, which are short-circuited by conductor 1, an alternative path of relatively low resistance is formed between electrodes the short-circuited bars 4. By suitably positioning bars 4- with respect to electrodes 9 and II and giving them a suitable size, the combined resistances of the respective paths between the three electrodes 9, I0 and Il can be made equal and the loads on the three phases of the current are also made equal to one another.

Since the resistance between two electrodes, either directly through the bath or through bars 9 and Il through' such as 4, depends upon the size of the electrodes fied in a gener-al manner and must be determined for each particular case. Furthermore, when two or moreshort circuited bars are employed to vary the current density, it may be advantageous to place them outside of the region extending between the electrodes immersed in the bath.

In the arrangement illustrated by Figs. 5 to 7, the bars 4 are so located as to provide for the heating of the glass in the vertical zones above the bars. However, when it is desired to concentrate the heating eii'ect tol aY horizontal layer in the mass of glass, we may make use of one of the arrangements disclosed by Figs. 8, 9, 10 and 11.

In the embodiment of Fig. 8, bars 4, which are short-circuited by conductor 1, considerably reduce the ristance between electrodes 9 and Il, while the resistance between electrodes 9 and l0 and between electrodes I 0 and II is also reduced, but to a much `lesser extent. .'Ihereby, the loads on the phases may be equalized while the power without appreciably altering the resistance between electrodes 9 and I0 and electrodes I 0 and Il In the embodiment of Fig. 10, bars 4 are unsymmetrically arranged, so that one bar I is located between electrodes i and il, while the bar I is located beyond electrode Il. This arrangement may be' employed to compensate for the difference in the" respective resistances in the paths between electrodes i and Il and electrodes Il and il due, for instance, to diiferences in their respective sizes or. in the distances between them.

In the embodiment of Fig. 11,` three bars l are employed, all three connected together by means of conductor 1. Two of these bars are positioned respectively on either side of electrode ii so as to make the resistance between this electrode and bars l lower than between electrode I and the4 bars. In this way, the heating close to electrodes i and Ii can be made diiferent.

In the above description of Figs. 2 toll, it has been assumed that bars l are shcrt-circuited so as to be substantially at the same potential,

. which is advantageous for the sake of economy and equality of power factor `in the dierent phases. However, resistance or self-induction might be inserted in conductor l so-as to vary the distribution of current between the electrodes. Such an arrangement permits of controlling the distribution of current through the bath bymeans located outside of the furnace.

Of course, while the invention has been described more'specifically with reference to the treatment of a bath of molten glass, it is also applicable to the heating, due to the flow of the current through the liquid, of other liquids which are good conductors of electricity, such as salt solutions and soon.

The invention can be applied with any form of polyphase current, such as three-phase current with four electrodes, or two-phase current.

The conducting bodies, which constitute an essential feature of the present invention,v may have form, position and number adapted to effect the desired variation of current density or heating ln a given zone ot the bath.

In a general manner. while we have, in the above description, disclosed what we deem to be practical and efficient embodiments of the present invention. it should be well understood that we do not wish to be limited thereto as there might be changes made in the arrangement, d isposition and form of the parts without departd ing from the principle of the present invention as comprehend'ed within the scope of the appendedclaims.

What we claim is:

l. An electric furnace of the type described, for the heating of' a liquid, which comprises, in

combination, a vessel containing said liquid, at

least two electrodes adapted to supply current to said liquid and extending from one wall to the opposite wall of said vessel, and at least one body, of higher electrical conductivity than said liquid and devoid of electrical connections to any source of electrical `energy expt through said liquid,

said body being 'immersed in saidtliquid betweenv said electrodes and spaced away from said walls.

`2. Anelectric furnace of the type described, which comprises, in combination, a vessel containing the liquid to be heated, at least two elec trodes of diiferent polarities adapted to supply current to said' liquid extending each from one wall-to' the other of said vessel and both located in a plane extending below the-surface of the liquid in said vessel, and at least one body, of higher electrical conductivity maasaiduquid, im-

mersed therein between said electrodes substantially inA said plane, said body extending parallel to said electrodes and being spaced away from said walls and devoid of electrical connections to any source of electrical energy except through said liquid.

3L A glass `making furnace comprising a vessel for containing a molten fluid mass, at least two electrodes of different polaritiesimmersed in said mass for supplying electrical current thereto, and at least one body having higher electrical conductivity than said molten mass immersed in thel electrodes adapted to supply electrical current to said molten mass, each of said electrodes extending from one wall of said vessel to the opposite wall thereof and being wholly below the surface of said molten mass, and at least one body hav;

`ing higher electrical conductivity than said molten mass immersed in the latter between said electrodes in the normal path of electric current from one electrode to the other and so mounted in the vessel that said mass is free to flow over the top of and below the same, said body being devoid of electrical connections to any source of electrical energy except through said mass.

5. A glass making furnace, comprising a vessel for containingva molten glass mass. at least two electrodes of different polarities contacting said mass for supplying electric current thereto, and at least one body having higher electrical conductivity than said molten glass mass immersed in the latter between said electrodes, said body being elongated and disposed horizontally in said vessel and supported at the ends thereof so as to permit free flow of the mass completely around said body in contact with the longitudinal surfaces thereof, said body being devoid oi.' electricalconnections to any source of electrical energy except through said mass;

6. A glass making furnace, comprising a vessel for containing a molten glass mass, at least two said electrodes. said body being horizontally dis- A posed with thelongitudinal axis thereof extending transversely of the furnace and being so mounted with relation to the furnace walls that vsaid mass may now freely around the periphery i of the portion thereof within the vessel, said body being Vdevoid of electrical connections to any mass.

1. A glass making furnace, comprising a vessel for containing a molten glass mass, at least two electrodes in contact. with said mass and loo nlnected to different terminals of a source of electrical energy for supplying electric current to said mass for heating the latter, and at least one vbody having higher electrical conductivity than said mass immersed therein in the path 4of electric current flowing between two of said electrodes 'and spaced from the bottomoi'. the vessource of electrical energy except through 'saidV 5 for containing glass in 45 trical connection with any 00 in spaced relation to the tom of the vessel and supported at their ends so teroonnecting said bodie sel, said body being devoid of electrical connections to any source of electrical energy except through said mass and being supported at its ends in said vessel so that said mass is `free to flow completely around the portion thereof within the vessel, the surface area' of said body in contact with said mass being relatively lsmall to provide a relatively greater 'electric current density in the zone immediately surrounding said body than in other parts of the mass.

8. A glass making furnace, comprising a vessel for containing a molten glass mass, at least two electrodes in contact with said mass and .connected to different terminals of a source of electrical energy for supplying electric current to said mass, at least one body having higher electrical conductivity than said mass tween said electrodes, the only electrical connection between said body and a source of electrical energy being said glass mass and said electrodes,- said electrodes and body being elongated and extending horizontally and parallel to one another across the width of said vessel wholly below the surface of said mass so' that the latter is free to flow entirely around the same and contact the entire surfaces thereof intermediate their ends within the vessel, the surface areas of each of said electrodes and body in contact with said mass being suiciently small to provide a large electrical currentdensity in the zones adjacent said electrodes and body, thereby creating higher temperatures in said zones than elsewhere in the mass.

9. A glass making furnace, comprising a vessel a liquid state, at least two electrodes of different polarities immersed in said glass for supplying electrical current to the latter, said electrodes being spaced from each other and extending across substantially the entire 40 width of said vessel, and at least one body having higher electrical conductivity than said glass immersed therein between said electrodes and mounted so that the glass .may flow over the top of and below the same, said body having no elecsource of electrical energy .except through said materials and electrodes, the surface areas of each of said electrodes and said body being such that the electric current density in said glass mass is greatest in the zones immediately surrounding said electrodes and body.

10. A glass making furnace, comprising a vessel for containing a molten glass mass, at least two electrodes of different' polarities contacting said mass for supplying electrical current thereto,

. at least two elongated, horizontally disposed bodies of higher electrical conductivity than said 'masa said bodies extending across the width of Asaid vessel and being immersed within said mass electrodes and the botas to permit free now of the mass completely A around said bodies in contact with longitudinal Isurfaces thereof, and anelectrical conductor insaid bodies -being in the path of electric current between said electrodes and devoid of electrical connections to any source of electrical energy except .through said in said vessel be` immersed therein mass, said conductor being devoid of electrical connections, to any source of electrical energy except through said bodies.

11. A glass making furnace comprising a vessel for containing a molten glass mass, at least two electrodes of different polarities contacting said mass for supplying electrical current thereto, at least two horizontally disposed bodies of higher electrical conductivity than said mass immersed in the latter and supported at their ends to exacross the normal between said electrodes, and an electrical conductor interconnecting said bodies, said bodies being devoid of electrical connections to any source of electrical energy except through said mass, said conductor being devoid of electrical connection to any source of electrical energy except through said bodies.

12. An electric furnace of the type described for the heating of a liquid, which comprises, in combination,` a vessel containing said liquid, at least three electrodes adapted to supply polyphase into said liquid, arranged so that the respective resistances of the liquid paths in the different phases are different, two bodies each of necting said two bodies. f

13. An electric furnace of the type described r the heating of a liquid, which comprises, in

combination, a vessel containing said liquid, at least three electrodes adapted to supply threephase current into said liquid and located substantially in a. horizontal plane, two bodies, each of higher electrical conductivity than said liquid,

close to the two extreme electrodes respectively, and a conductor interconnecting said two bodies.

14. An electric furnace of the type described for the heating of a liquid, which comprises, in combination, a vessel containing said liquid, three adapted to supply plane, and a conductor interconnecting said two bodies; i

15. An electric furnace of the type described for the heating of a liquid, which comprises, in combination, a vessel containing said liquid, three electrodes adapted to supply three-phase current into said liquid and located` substantially in a horizontal plane, two bodies, each of higher electrical conductivity than said liquid, immersed therein EDOUARD vlaams nonni.. l YvAN rayonne. 

